advice for locally advanced Pca

Tang,

Welcome to the board. I think you're doing well in researching before any decision. In any case the basic data in hand, serving in the judgment must be reliable. Confirming the diagnosis should be your first step, in particular if you opt for RT in a setting of apparent extraprostatic extensions, inspite of the experienced urologist's recommendation for ADT as solo therapy (what may be his reasoning?). In other words, you need to locate those metastases that will become the targets for radiation.

The article of your link refers to cases where radiation only has debulked cancer (shrinking the whole volume) therefore extending the life of patients. This is typical occurrences in patients with extraprostatic disease (including salvage treatments for RP) where the treatment is usually done on guessing (no precise targets to aim). 
RT works very well when the cancer is contained or when it is localized so that the radiologists can use reference data from traditional image exams (CT, MRI, Bonescan) to decide on the field of attack. They imagine the whole gland as a tumor and the surrounding area that would be zipped at the prostate bed, iliac lymph nodes and bone. Far metastases are subjected to spot radiation and must be located at convenient locations to avoid superimposing rads in areas already radiated. This is a difficult treatment that needs particular attention in isodose planning, but it could eliminate the bandit successfully.
As you can think, a reliable image exam is crucial in the decision (your dad's case). The best at present times is the PSMA PET scan which, if in your shoes I would do it before advancing with anything.

The info you share above classifies your dad with a T3b but the "gross extraprostatic extensions" could include invaded seminal vesicles (T3c) or even more extensions at the levator muscles and pelvic wall, turning his case into a T4. I do not know why but Gleason score 8 (4+4) cases have the history for being difficult to treat. My lay opinion on 4+4 cases is that they represent micrometastases of an aggressive type of cancer. In my researches I found that typically these (4+4) produce low levels of PSA serum when at soft tissue but high levels when at bone or LN. Your dad got a PSA of 28 ng/ml and an apparent LN metastasis (N1 2cmx3.4cm) that, in my lay opinion, could justify the high PSA. This is considered a High Risk case
The missing info regards distant metastases (M0) and in such respect I would be suspicious of the bone scan results. M0 could be guessed as M1b, and that leads to the conclusion of his doctor in recommending ADT. A better nuclear image specific for PCa in bone (PET FDG) could give you a better understanding on the extent of the disease.

Unfortunately, treatments for PCa cases with metastases not localized are considered systemic and to such extent palliative (extending the life of the patient with the prime goal in the quality of life). Most doctors recommend ADT and chemo, however there are some cases where the patient has a fewer number of metastases that can be treated with intent of cure with a combination of ADT+ Chemo plus spot RT. This is called oligometastatic treatment.

I had a look into  Dr. Richard F. Cohen past experiences and found several papers on head RT issues. Did not find any about PCa but surely as an experienced radiologist he (or his team) can do the job properly. The machine delivering the rays and the equipment for IGRT is important in terms of delivery accuracy (lesser risk for collateral damage). 4D CT may be better than 3D CT but it would not change the results regarding the elimination of the cancer. I would chose a radiologist experienced in PCa cases working at modern facilities.

ADT main role in the combination therapy of RT+ADT is to sensitize the cells into absorbing the radiation. It affects cells AR and also provides a stable cell's life cycle preferred for the success of radiation in destroying its DNA. From clinical studies one knows that it improves the RT by approximately 35%.
In such regards, ADT is best if started two month in advance of RT and continued at least six month after RT (the typical period of cell's life cycle). Some doctors prefer longer periods after RT, lasting two years in high risk cases. In my lay opinion six month is sufficient for therapy efficacy. ADT will also mask the PSA so that one needs to wait till it looses its effects to verify the success of the treatment.
In my case of SRT I did radiation alone (clean environment) so that I could certify the outcome the soonest. Once failure was confirmed I started ADT.

Here are links regarding the image studies;

http://emedicine.medscape.com/article/387840-overview

https://link.springer.com/chapter/10.1007/978-0-387-48902-5_32/fulltext.html

https://www.ncbi.nlm.nih.gov/pubmed/25738559

Your dad could try involvement in a clinical trial, free of charge, for a PSMA PET scan that would give you a conclusive posture to a final decision. You can discuss to access possibilities with his doctor. Here is the link;

https://clinicaltrials.gov/ct2/show/NCT02282137

Best wishes and luck in his journey.

VGama